Corrosion Protection of Cables in a Concrete Structure

ABSTRACT

Steel reinforcing cables in concrete are protected against corrosion by injecting a carrier fluid and corrosion inhibitors into interstitial spaces between the wires of the cable at a first location along the cable and causing the fluid to pass through the interstitial spaces between the wires of the cable to a second location along the cable. The cable comprises an array of wires confined together and intimately surrounded by a covering material which is engaged with a periphery of the cable so that there are insufficient interconnected spaces between the cable and the covering material to allow passage of fluid longitudinally along the cable outside the cable itself. The method can be used with pre-stressed concrete, with post-tensioned bonded cables and with extruded un-bonded mono-strand cables.

The present invention relates generally to the field of pre-stressed orpost-tensioned concrete structures, and more particularly, to a methodfor protection of steel cables susceptible to corrosion in such concretestructures.

BACKGROUND OF THE INVENTION

Pre-tensioning of concrete is a method for improving the load carryingcapacity of concrete structures. It can be used to produce beams, floorsor bridges with longer spans and less deflection using thinner sectionsthan is practical with ordinary reinforced concrete. Tendons used forpre-tensioning are generally made of high tensile steel cables and areused to provide an initial compressive load which produces a compressivestress that balances some or all of the tensile stress that the concretemember would otherwise experience due to a bending load. Pre-tensioningcan be accomplished in three ways: pre-stressed concrete, and bonded orun-bonded post-tensioned concrete.

Pre-stressed concrete is cast around already tensioned cables. Thismethod produces a good bond between the cable and concrete, which bothprotects the cable from corrosion and allows for direct transfer ofloads between the cable and the concrete. The cured concrete adheres andbonds to the cables and when the load on the cables is released, much ofit is transferred to the concrete as compression by static friction.However, it requires stout formwork and anchoring points between whichthe cable is stretched and held prior to the placement of the concrete.The cables are usually in a straight line unless deviators are installedin which case the cable will typically have straight segments. Mostpre-tensioned concrete elements are prefabricated in a factory and mustbe transported to the construction site, which limits their size.Examples of pre-stressed elements include balcony elements, lintels,floor panels, double tees, beams and foundation piles.

Bonded post-tensioned concrete is the descriptive term for a method ofapplying compression after pouring and curing the concrete. The concreteis typically cast around a duct, which may be of plastic, steel oraluminium. The ducts are often curved or draped to follow the profilewhere they will provide the greatest structural benefit. One or morecables are generally fished through the duct after the concrete ispoured. Once the concrete has hardened, the cables are tensioned byhydraulic jacks that react against the concrete member itself. When thecables have been tensioned sufficiently, they are wedged or clamped inposition to maintain tension in the cables and compression in theconcrete after the jacks are removed. The duct is then filled with agrout to protect the cables from corrosion.

Un-bonded post-tensioned concrete differs from bonded post-tensioning byproviding each individual cable permanent freedom of movement relativeto the concrete. To achieve this, each individual cable is typicallycoated with grease and enclosed by a plastic sheathing. In some casesthe cable is a loose fit inside the sheath with the intention that thegrease fills the space between the cable and the sheath. Thisconstruction can be formed by inserting the cable from one end into apre-formed tubular sheath with the space between them being sufficientto allow the insertion to occur. In other cases the sheath is formed bycovering the cable and surrounding grease with a strip of the coveringmaterial which is bent around the cable and then sealed or welded alonga longitudinal seam to surround the cable.

In both cases the intention is that the cable is coated with grease andis sealed to prevent moisture entry and to ensure that the steel cableis maintained in a moisture free environment. In practical operationvoids are typically present in this type of construction.

In another manufacturing system which is more typically used today forun-bonded mono-strand tendons, the cable is covered by grease and aplastic sheath is extruded onto the exterior of the cable as a tightenvelope. In this case there are typically no voids and no path aroundthe cable for moisture or other material to migrate along the sheath.

It is also intended that the sheath be continuous, complete and moistureimpermeable. In practice the sheath is often damaged by its introductioninto the forms, by failure to seal the ends of the sheath, or by thetensioning of the cable so that moisture can enter. Thus in thetheoretical world, no moisture can enter into or migrate along thesheath so that no corrosion can occur. In practice corrosion typicallydoes occur even to the extent of causing catastrophic failures if notdetected and remediated.

The transfer of tension to the concrete is achieved by the steel cableacting against steel anchors embedded at the end of each cable. The maindisadvantage over bonded post-tensioning is the fact that a cable cande-stress itself and burst out of the slab if damaged (such as duringrepair on the slab). The advantages of this system over bondedpost-tensioning are:

a) The ability to individually adjust cables based on poor fieldconditions (For example: shifting a group of four cables around anopening by placing two to either side),

b) The procedure of post-stress grouting is eliminated, and

c) it is possible to de-stress the cables before attempting repair work.

In U.S. Pat. No. 5,365,779 (Vander Velde) issued Nov. 24, 1994 there isdisclosed a method and apparatus for the corrosion condition evaluationof un-bonded pre-stressing elements in post-tension concrete structures.The method involves locating a pre-stressing element in the structureand providing at least two openings in the structure at positions alongthe length of the element. One of the openings is an inlet port and theother is an outlet port, each of the ports permitting communication withthe gaseous environment within a conduit surrounding the pre-stressingelement. The gaseous environment is accessed through the outlet port byextracting a sample of gas therethrough. The sample is then measured todetermine its humidity and thereby evaluate the corrosion condition ofthe pre-stressing element between the inlet port and the outlet port. Amethod and apparatus is also provided for the on-site corrosionprotection of the un-bonded pre-stressing elements whereby the gaseousenvironments within the conduits are cyclically pressurized with a drygas for extraction of moisture which may lead to corrosion.

However as set forth in the above patent, the use of this method islimited to un-bonded post tensioning systems where there is enough spacebetween the cable and its surrounding sheath to form a conduit to allowthe passage of gas for sampling and for later drying if necessary orselected. WO 87/06958 assigned to Precision Dependability and QualityTesting discloses a method of treating a reinforced structure of masonryor cementitious material, such as concrete, to inhibit corrosion of thereinforcement. The method comprises inserting within the said material avapour phase corrosion inhibitor so that the inhibitor migrates throughthe porous structure of the said material, and more-particularly alongthe interface between the said material and the reinforcement, toprotect the reinforcement.

Again in this method there must be a channel or path around thereinforcement within the material to allow the passage of the vapourphase inhibitor.

However in regard to the other pre-tensioning methods defined abovethere is no channel or path for the passage of the protective fluid sothat the above methods are not possible with such constructions.

The disclosures of the above patents are incorporated herein byreference.

This method of the present invention relates to the pre-tensioningsystem where the cable is intimately surrounded by the concrete itself.

This method of the present invention relates to the un-bondedpost-tensioning system where the cable is contained within an extrudedplastic sleeve extruded onto the cable and extending along the concretemember and there is provided an un-bonded filler material, generallygrease, between the cable and the sleeve arranged to allow sliding ofthe cable within the sleeve during tensioning;

This method of the present invention relates to the bondedpost-tensioning system where the cable is contained within a tubularcontainer extending along the concrete member and the cable isintimately surrounded by a filler material, generally a cementitiousgrout, inserted into the tubular container after tensioning of the cablewithin the tubular container so that the grout is bonded intimately tothe wires of the cable. Often multiple cables are installed in a singletubular container and the grout filler material fills and bondsintimately to all of the cables within the duct.

These methods now constitute a significant proportion of the installedpre-tensioned reinforcing systems so that a majority of thepre-tensioned structures cannot be protected using the methods of theabove patents.

SUMMARY OF THE INVENTION

It is one object of the present invention therefore to provide a methodfor use with a steel reinforcing cable embedded in a concrete memberwhich can be used to detect and/or treat corrosion of the cable in theconcrete member.

According to a first aspect of the invention there is provided a methodfor use with a steel reinforcing cable embedded in a concrete member;

wherein the cable comprises an array of wires extending along theconcrete for providing reinforcement thereto;

wherein the cable is intimately surrounded by a covering material whichis engaged with a periphery of the cable so that there are insufficientinterconnected spaces between the cable and the covering material toallow passage of fluid along the cable between the cable and thecovering material;

the method comprising inserting a fluid into interstitial spaces betweenthe wires of the cable at a first location along the cable and causingthe fluid to pass through the interstitial spaces between the wires ofthe cable to a second location along the cable.

The present Applicant has found totally surprisingly that even in asituation where there is no path around the cable as required by theabove prior art methods, there is a sufficient path within theinterstices of the wires of the cable itself, even when under the highloads necessary for tensioning the concrete, to allow effectivequantities of a fluid to pass along the cable.

In most cases, the fluid is selected so that it provides propertiessuitable to reduce corrosion of the steel wires of the cable.

In this case the fluid can contain corrosion inhibiting material such ascorrosion inhibiting materials selected from the group consisting of:

Amines

Amino alcohol;

Amino carboxylate;

Calcium sulfonate;

Organofunctional silane, siloxane or silicone

Grease amine

Oil amine

Amine salts with nitrous or chromic acids,

Amine salts with carbonic acid, carbamic acid, acetic acid, substitutedbenzoic acids and organic esters of nitrous acid, phthallic acid orcarbonic acid,

Primary, secondary and tertiary aliphatic amines,

Cycloaliphatic and aromatic amines,

Polymethylene amines,

Calcium nitrite, sodium nitrite,

mixtures of nitrites, urea, hexamethylene tetramine and ethanolamines,or

Nitrobenzene and 1-Nitronaphthalene.

Preferably the corrosion inhibiting material is Calcium sulfonate orOrganofunctional silane.

The fluid can contain also or as an alternative Vapor Phase Inhibitorswhich are provided as a solid or liquid and have the properties ofevaporation to provide a material which condenses into requiredlocations to act as a corrosion inhibitor.

The carrier fluid can be a liquid or can be a gas. Where a gas is usedthis can operate as a drying agent to drive off any moisture from thearea within or around the cable. Where a liquid is used this istypically a non-water-based liquid so as to avoid adding additionalwater which may be detrimental to the corrosion process or to drive outmoisture by impregnating the volume around the cable with the liquiditself. The liquid or other carrier fluid may be selected to react withany water which may be present. If a water-based liquid is used,sufficient inhibitor or the use of some type of drying or othercorrosion mitigation technique is recommended to minimize the risk ofaccelerating the corrosion of cables which may be contaminated with saltor otherwise already corroding.

Thus the liquid can be arranged to expel moisture from the interstitialspaces between the wires of the cable. In some cases depending on thesurrounding material at the cable, the liquid can be arranged togenerate an impregnated zone which can be hydrophobic at or around thecable by diffusing or spreading outwardly from the cable into thesurrounding covering material so as to generate a hydrophobic zonearound the cable.

In some cases the fluid interacts with the covering material to changeits properties within the impregnated region.

In some cases the fluid interacts with the covering material to reducepermeability of the impregnated region.

In some cases the fluid interacts with the covering material to increasethe electrical resistivity of the impregnated region.

In some cases the fluid forms a protective film on exposed portions ofthe wires.

In some cases the liquid is an oil or silicone based material generallyof low viscosity which acts to displace any moisture and to fill anyinterstices where moisture may return thus preventing further corrosion.In other cases, the liquid may be selected so that it is arranged toincrease in viscosity so that it remains more effectively in thelocation to which it has reached during the insertion process or toset-up to form a solid after inserting into the cable.

For example the liquid may be selected from the group consisting of

Silane, siloxane, silicone;

Oil

Alcohol or other organic solvent

Polymer resin

In some cases the liquid may also be the corrosion inhibiting materialsuch as organofunctional silane, calcium sulfonate or amino alcohol. Theliquid may also be water as described above.

In another arrangement as set out above the fluid comprises a gasarranged to effect a drying action on the wires of the cable to expelmoisture from the interstitial spaces between the wires. Continuedapplication of dry gas to the interstitial spaces between the wires mayalso dry the surrounding covering material over time. The introductionof gas may be used in a testing procedure to drive moisture ormoisture-laden air from the interstitial spaces between the wires, whichgas is then collected at the second location for analysis of a moisturecontent thereof. In this way an initial testing procedure can beprovided which detects the presence of moisture and then goes onto aremediation process if moisture is detected.

In accordance with a second aspect of the invention, there is provided amethod for use with a steel reinforcing cable embedded in concrete;

wherein the cable comprises an array of wires extending along theconcrete for providing reinforcement thereto;

wherein the wires of the cable are intimately surrounded by theconcrete;

the method comprising inserting a fluid into interstitial spaces betweenthe wires of the cable at a first location along the cable and causingthe fluid to pass through the interstitial spaces between the wires ofthe cable to a second location along the cable. Thus in this case themethod is used with pre-stressed cables where the cable is buried intothe concrete as the concrete is set.

In accordance with a third aspect of the invention, there is provided amethod for use with a steel reinforcing cable embedded in a concretemember;

wherein the cable comprises an array of wires extending along theconcrete member for providing reinforcement thereto;

wherein the cable is contained within a tubular container extendingalong the concrete member;

wherein the wires of the cable are intimately surrounded by a fillermaterial inserted into the tubular container after tensioning of thecable within the tubular container where the filler material is bondedintimately to the wires of the cable;

the method comprising inserting a fluid into interstitial spaces betweenthe wires of the cable at a first location along the cable and causingthe fluid to pass through the interstitial spaces between the wires ofthe cable to a second location along the cable.

Thus in this case the method is used with post tensioned bonded cableswhere the cable is buried in a grout injected into the tubular sleeveafter tensioning.

In accordance with a fourth aspect of the invention, there is provided amethod for use with a steel reinforcing cable;

wherein the cable comprises an array of wires confined together to forman elongate cable;

wherein the cable is contained within an extruded plastic sleeveextruded onto the cable so as to enter into external interstices betweenthe wires around the cable;

the cable and the plastic sleeve extending along the concrete member;

wherein there is provided an un-bonded filler material in the externalinterstices between the cable and the sleeve arranged to allow slidingof the cable within the sleeve during tensioning;

the method comprising inserting a fluid into interstitial spaces betweenthe wires of the cable at a first location along the cable and causingthe fluid to pass through the interstitial spaces between the wires ofthe cable to a second location along the cable.

Thus in this case the method is used with post tensioned un-bondedcables where the cable is contained within an extruded plastic sleeve.

In accordance with a further aspect of the invention, there is provideda method for use with a steel reinforcing cable embedded in a concreteor mortar or grout covering material;

wherein the cable comprises an array of wires confined together to forman elongate cable extending along the concrete for providingreinforcement thereto;

the method comprising introducing a liquid into the interstitial spaceswithin the cable at a first location along the cable and causing thefluid to pass along the cable to a second location along the cable;

and causing the liquid arranged to spread outwardly from the cable toimpregnate into the surrounding covering material so as to generate animpregnated zone around the cable.

This impregnated zone may be hydrophobic, it may be impregnated withcorrosion inhibiting material, or it may be impregnated to provide highelectrical resistance. The impregnation of the covering material mayotherwise modify the properties of the covering material such asproviding reduced porosity, reduced permeability, waterproofing orincreased strength.

Thus in this aspect, the injection of the liquid such as oil, aminoalcohol, calcium sulfonate or silane has been found to cause the liquidto diffuse or migrate outwardly into a surrounding volume of concrete ormortar surrounding the cable to form a generally cylindrical impregnatedzone around the cable. In the case of injection of silane basedmaterial, the reaction of the silane with the concrete has created ahydrophobic layer of concrete surrounding the cable into which it isdifficult for moisture to penetrate.

The injection of the fluid into the cable can occur at ends of the cablewhere the wires of the cable are exposed so that the injection occursdirectly into the interstices between the wires. In this case the secondlocation may be at the other end or may be at an intermediate location.Alternatively, surprisingly, injection of the fluid into the cable canoccur at an intermediate location of the cable is also possible wherethe injection is at the periphery of the cable requiring the fluid topenetrate from the periphery into the interstices between the wires.Both techniques have been shown to operate satisfactorily.

The injection typically will require some pressure but this has beenfound that a relatively low pressure of the order of 50 to 100 psi forlow viscosity liquids are suitable to travel the length of the cable,coat the exposed steel surfaces, impregnate the concrete surrounding thecable, drive off moisture and carry the corrosion inhibitor. Higherpressures may be required for longer lengths, higher viscosity liquidsor semi-liquid materials such as grease. Vacuum can be used at thedownstream end either in addition to or as a replacement to thepressurized supply. Gas can be injected in the same manner either as airfor drying or as a vapor for vapor deposition of Vapor Phase Corrosioninhibitors.

The ends or intermediate locations may be already exposed or may belocated by drilling to the cable or by other excavation methods.Intermediate locations may be excavated to expose one face of the cableor the excavation may extend around the periphery of the cable.

Various inhibitors may be used in the method of the invention, providedthey are chemically suited to inhibiting corrosion of whateverreinforcement is used. The inhibitor for ferrous metal reinforcement mayfor example be, or include, at least one material selected from

-   -   (i) Amine salts with nitrous or chromic acids,    -   (ii) Amine functional groups attached to polymer chains        including alcohols and silanes,    -   (iii) Amine salts including those with carbonic acid, carbamic        acid, acetic acid, substituted benzoic acids and    -   (iv) organic esters of nitrous acid, phthallic acid or carbonic        acid,    -   (v) Primary, secondary and tertiary aliphatic amines,    -   (vi) Cycloaliphatic and aromatic amines,    -   (vii) Polymethylene amines,    -   (viii) nitrite salts, mixtures of nitrites with urea,        hexamethylene tetramine and ethanolamines, or    -   (ix) Nitrobenzene and 1-Nitronaphthalene,    -   (x) Calcium and other sulfonates,    -   (xi) Organofunctional silanes and siloxanes.

The corrosion inhibitor can be in liquid form or may be a Vapor PhaseInhibitor (VPI). The preferred VPI's for protecting ferrous metal(usually steel) reinforcement by the method of the present invention aredicyclohexylamine nitrite (DCHN), cyclohexylamine benzoate (CHAB) andcyclohexylamine carbamate (CHC), more preferably a mixture of CHAB andCHC. These are both white solids and have the following structures: CHABO—NH3+02C CHC NH3+O—C—NH—0 Mixtures of fast-acting and slow-acting VPI'shave the advantage of combining fast initial action with extendedservice life. Thus the inhibitor preferably comprises at least twovapour phase inhibitor compounds, at least one of which vaporisesrelatively slowly and at least one other of which vaporises relativelyquickly under the conditions to be encountered by the concrete structurein service.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view transversely through aconcrete member at an injection site for a fluid into the interstices ofa reinforcing pre-stressed cable in a method according to the presentinvention.

FIG. 2 is a vertical cross-sectional view longitudinally through aconcrete member at a bonded post-tensioned reinforcing cable showingfluid injection into ends of the cable in a method according to thepresent invention.

FIG. 3 is a cross-sectional view through the cable and surroundingsleeve of the concrete member of FIG. 2,

FIG. 4 is a cross-sectional view through an un-bonded post-tensionedcable with surrounding plastic sleeves showing the interstices of thecable containing the injected fluid.

DETAILED DESCRIPTION

In FIG. 1 is shown a pre-stressed steel reinforcing cable 10 embedded ina concrete member 11. The cable 10 comprises an array of wires 12confined together and under tension. Typically the wires are woundaround a helix at a shallow angle so as to hold them as a confined arraywith each wire butting against its neighbours and held in contact withits neighbours by the loads therebetween generated by the tension on thehelical array. Thus each wire has its surface in direct contact with itsneighbour along its length as indicated at 13.

In the pre-stressed system shown in FIG. 1, the cable is intimatelysurrounded by the concrete itself by casting of the concrete while thecable is in place in the form so that the concrete is engaged with aperiphery of the cable at the peripheral surface of the outermost wires.Thus the concrete in the casting process butts intimately with all ofthe peripheral surfaces of the wires and prevents the formation of anyspaces around the cable to allow passage of fluid longitudinally alongthe cable in spaces between the cable and the covering material. Thusthere are in effect no interstitial spaces and certainly nointerconnected interstitial spaces between the cable and the coveringmaterial itself.

However the wires themselves remain separate and leave interstitialspaces 15 between each wire and its neighbours. The method of thepresent invention therefore comprises inserting a fluid 16 into theinterstitial spaces 15 between the wires of the cable.

The fluid is injected or inserted at a first location along the cableand the fluid is caused to pass through the interstitial spaces betweenthe wires of the cable to a second location along the cable. Thelocation in FIG. 1 is at a position along the length of the cable sothat a hole 17 is drilled to intersect the cable from a surface 18 ofthe concrete member to the cable so that one side face of the cable isexposed in the hole. A tube 19 is inserted into the hole and held inplace by an adhesive or by a suitable coupling 20 which holds the tubein place to resist the pressure in the fluid tending to displace thetube. Alternatively, the hole may be excavated and may extend around theperiphery of the cable at the location of the excavation. Many differentmounting arrangements can be used and one example only is shown where aflange 21 is fastened to the surface 18 by screws 22.

The fluid 16 is provided by a pressurized container 23 which is attachedto the tube. The container can be of any arrangement depending on thepressure to be applied. In one example the pressure is of the order of50 to 100 psi which requires only a plastic container with a hand pumpfor generating the pressure. In other cases a pressure pump, pressurepot, piston pump, gear pump, hydraulic cylinder or compressor may beused to generate the required fluid pressure to enable the material toflow. Depending on the type of pumping and associated measuring devices,the applied pressure and flow rate can be adjusted and monitored.Intermediate holes can be provided to monitor the movement of the fluidalong the length of the cable or to progressively insert the fluid intothe cable, section by section to minimize the distance the fluid isrequired to flow from each injection location. Vacuum may be applied ata position separate from the point of application of the fluid to assistin flow and penetration of the fluid along the length of the cable.

The fluid 16 at the side face of the cable can penetrate between thewires into the interstices 15 into the interstices of the wires withinthe cable itself. From those interstices the fluid can pass along thecable to a second location. The second location not shown in FIG. 1 canbe at an end of the cable or can be at another intermediate location onthe cable. In order to complete protection of a long length of cable, anumber of locations along the cable can be selected and fluid injectedto pass along the cable to a next location.

The fluid 16 is selected as defined above so that it includes a carrieras defined and a corrosion inhibitor as defined which providesproperties suitable to reduce corrosion of the steel wires of the cable.The corrosion inhibitor may improve the durability of the structure byimproving or modifying the properties of the surrounding concrete. Thecarrier and the corrosion inhibitor may in some cases be the samematerial.

In FIG. 1 the fluid includes a liquid carrier which may expel moistureor react with moisture from the interstitial spaces 15 between the wiresof the cable and impregnate the surrounding concrete to generate ahydrophobic zone 24 around the cable by diffusing or spreading outwardlyfrom the cable into the surrounding concrete. The fluid may also act tocoat the wires and form a protective film on the surface of the wires.The interior wire surfaces may be largely or fully coated. The exteriorwire surfaces in direct contact with the surrounding concrete and mayreceive only a partial protective film coating. The use of a fluid whichacts to coat the wires and form a protective film is particularlybeneficial to provide corrosion protection to steel wire surfaces whichare exposed to air bubbles, voids or pockets in the surroundingconcrete, grout or filler material at certain points along the length ofthe cable. The fluid can reach these bubbles, voids or pockets via theinterstitial spaces even though they are not interconnected through thecovering material.

Thus the injection of the carrier liquid such as oil, amine, aminoalcohol, calcium sulfonate, silane, siloxane, silicone, organic solventor other polymer causes the liquid to diffuse or migrate outwardly toimpregnate into a surrounding volume of concrete or mortar surroundingthe cable to form a generally cylindrical impregnated zone around thecable. Depending on the material used it may be difficult for moistureto penetrate. The fluid may be free of water. The fluid can be selectedso that it interacts with the covering material to change the propertiesof the covering material within the impregnated region. Thus forexample, the fluid interacts with the covering material to reducepermeability of the impregnated region. Thus for example, the fluidinteracts with the covering material to increase the electricalresistivity of the impregnated region. Thus for example, the fluid formsa protective film on exposed portions of the wires. Thus for example,the impregnated zone around the cable includes a corrosion inhibitingmaterial. Thus for example, the impregnated zone around the cable has anincreased electrical resistance. Thus for example, the impregnated zonearound the cable has a reduced permeability.

In FIGS. 2 and 3, the method is used with a post-tensioned system inwhich the cable 30 formed by wires 30A with interstices 30B is containedwithin a tubular container 31 extending along the concrete member 32between the ends 34, 35. The wires of the cable are intimatelysurrounded by a filler material or grout 33 inserted into the tubularcontainer 31 after tensioning of the cable 30 within the tubularcontainer so that the filler material 33 is bonded intimately to thewires of the cable 30. In many cases multiple cables are present insidea singular tubular container (duct) wherein the filler materialsurrounds each of the cables. The duct assembly containing multiplecables is often referred to as a tendon or multi-strand assembly.

Again, the method comprising inserting a fluid into interstitial spaces30B between the wires of the cable at a first location at the end 35along the cable and causing the fluid to pass through the interstitialspaces between the wires of the cable to a second location at the end 34along the cable.

In FIGS. 2 and 3, the fluid comprises a gas from a pressurized supply 36arranged to effect a drying action on the wires of the cable to expelmoisture from the interstitial spaces between the wires. In this casethe gas may be used in a testing procedure to drive moisture from theinterstitial spaces between the wires, which is then collected at theend 34 (or an alternate location) at a sample extractor 37 at an outlet40 for analysis of a moisture content. In this way an initial testingprocedure can be provided which detects the presence of any moisture andthen goes onto a remediation process if moisture is detected.

A vacuum pump 38 can be provided connected to the outlet 40 to assist indrawing the gas more effectively along the path. A valve 39 controls theconnection of the outlet 40 to the sample collector 37 or to the vacuum38.

Similar to the previous example illustrated in FIG. 1, liquid can beinjected into the interstices and can provide benefits similar to theexample previously described.

In FIG. 4 the cable 40 comprises an array of wires 41 confined togetherto form an elongate cable with interstices 42 where the cable 40 iscontained within an extruded plastic sleeve 43 extruded onto the cable.There is provided an un-bonded filler material, typically grease 44,between the cable 40 and the sleeve 43 arranged to allow sliding of thecable within the sleeve during tensioning.

The intimate engagement of the extruded jacket or sleeve 43 and thepenetration of the inside surface of the sleeve into the exteriorinterstices of the wires around the cable causes the grease 44 to becontained or compressed onto the exterior surfaces around the wires 41of the cable both around the outside of the wires and into theinterstices between the wires so that there are no paths around thewires within the sleeve.

As explained and shown previously the fluid is injected intointerstitial spaces 42 between the wires of the cable 41 at a firstlocation along the cable and the fluid passes through the interstitialspaces between the wires of the cable to a second location along thecable.

1. A method for use with a steel reinforcing cable embedded in aconcrete member; wherein the cable comprises an array of wires extendingalong the concrete for providing reinforcement thereto; wherein thecable is intimately surrounded by a covering material which is engagedwith a periphery of the cable so that there are insufficientinterconnected spaces between the cable and the covering material toallow passage of fluid along the cable between the cable and thecovering material; the method comprising inserting a fluid intointerstitial spaces between the wires of the cable at a first locationalong the cable and causing the fluid to pass through the interstitialspaces between the wires of the cable to a second location along thecable.
 2. The method according to claim 1 wherein the fluid is selectedto reduce corrosion of the steel wires of the cable.
 3. The methodaccording to claim 1 wherein the fluid comprises corrosion inhibitingmaterial.
 4. The method according to claim 3 wherein the corrosioninhibiting material is selected from the group consisting of: AminesAmino alcohol; Amino carboxylate; Calcium sulfonate; Organofunctionalsilane, siloxane or silicone Grease amine Oil amine Amine salts withnitrous or chromic acids, Amine salts with carbonic acid, carbamic acid,acetic acid, substituted benzoic acids and organic esters of nitrousacid, phthallic acid or carbonic acid, Primary, secondary and tertiaryaliphatic amines, Cycloaliphatic and aromatic amines, Polymethyleneamines, Mixtures of nitrites, urea, hexamethylene tetramine andethanolamines, and Nitrobenzene and 1-Nitronaphthalene.
 5. The methodaccording to claim 3 wherein the corrosion inhibiting material isCalcium sulfonate or Organofunctional silane.
 6. The method according toclaim 1 wherein the fluid comprises a liquid arranged to expel moisturefrom the interstitial spaces between the wires of the cable.
 7. Themethod according to claim 1 wherein the fluid impregnates a region ofthe covering material surrounding the cable.
 8. The method according toclaim 7 wherein the fluid interacts with the covering material to changeits properties within the impregnated region.
 9. The method according toclaim 7 wherein the fluid interacts with the covering material to reducepermeability of the impregnated region.
 10. The method according toclaim 7 wherein the fluid interacts with the covering material toincrease the electrical resistivity of the impregnated region.
 11. Themethod according to claim 1 wherein the fluid forms a protective film onexposed portions of the wires.
 12. The method according to claim 1wherein the fluid comprises a liquid arranged to spread outwardly fromthe cable into the surrounding covering material so as to generate ahydrophobic zone around the cable.
 13. The method according to claim 1wherein the fluid comprises a liquid which is arranged to increase inviscosity after inserting into the cable.
 14. The method according toclaim 1 wherein the fluid is a liquid which is arranged to set-up afterinserting into the cable.
 15. The method according to claim 1 whereinthe fluid comprises a liquid selected from the group consisting of:Silane, siloxane silicone, Oil, Organic solvent, Calcium sulfonate, andPolymer resin.
 16. The method according to claim 1 wherein the fluidcomprises a liquid selected from the group consisting of: Water, Watercontaining dissolved salts, Water containing suspended particles. 17.The method according to claim 1 wherein the fluid comprises a gasarranged to effect a drying action on the wires of the cable to expelmoisture from the interstitial spaces between the wires.
 18. Methodaccording to claim 17 wherein the application of a gas is continued toeffect the drying of the covering material adjacent to the cable. 19.The method according to claim 1 wherein the fluid comprises a gasarranged to drive moisture from the interstitial spaces between thewires and wherein the gas and the moisture are collected at the secondlocation for analysis of a moisture content thereof.
 20. The methodaccording to claim 1 wherein the covering material is concrete where thecable is directly surrounded by the concrete of the concrete member. 21.The method according to claim 1 wherein the covering material is a groutwithin a tubular containment member.
 22. The method according to claim21 wherein more than one cable is present within the tubular containmentmember.
 23. The method according to claim 1 wherein the coveringmaterial comprises a jacket extruded onto the periphery of the cablewhich contains an un-bonded filler material to allow the cable to slideinside the jacket during tensioning.
 24. A method for use with a steelreinforcing cable embedded in concrete; wherein the cable comprises anarray of wires extending along the concrete for providing reinforcementthereto; wherein the wires of the cable are intimately surrounded by theconcrete; the method comprising inserting a fluid into interstitialspaces between the wires of the cable at a first location along thecable and causing the fluid to pass through the interstitial spacesbetween the wires of the cable to a second location along the cable. 25.A method for use with a steel reinforcing cable embedded in a concretemember; wherein the cable comprises an array of wires extending alongthe concrete member for providing reinforcement thereto; wherein thecable is contained within a tubular container extending along theconcrete member; wherein the wires of the cable are intimatelysurrounded by a filler material inserted into the tubular containerafter tensioning of the cable within the tubular container where thefiller material is bonded intimately to the wires of the cable; themethod comprising inserting a fluid into interstitial spaces between thewires of the cable at a first location along the cable and causing thefluid to pass through the interstitial spaces between the wires of thecable to a second location along the cable.
 26. A method for use with asteel reinforcing cable; wherein the cable comprises an array of wiresconfined together to form an elongate cable; wherein the cable iscontained within an extruded plastic sleeve extruded onto the cable soas to enter into external interstices between the wires around thecable; the cable and the plastic sleeve extending along the concretemember; wherein there is provided an un-bonded filler material in theexternal interstices between the cable and the sleeve arranged to allowsliding of the cable within the sleeve during tensioning; the methodcomprising inserting a fluid into interstitial spaces between the wiresof the cable at a first location along the cable and causing the fluidto pass through the interstitial spaces between the wires of the cableto a second location along the cable.
 27. A method for use with a steelreinforcing cable embedded in a concrete or mortar or grout coveringmaterial; wherein the cable comprises an array of wires confinedtogether to form an elongate cable extending along the concrete forproviding reinforcement thereto; the method comprising introducing aliquid into the interstitial spaces within the cable at a first locationalong the cable and causing the liquid to pass along the cable to asecond location along the cable; and causing the liquid arranged tospread outwardly from the cable to impregnate into the surroundingcovering material so as to generate an impregnated zone around thecable.
 28. The method according to claim 27 wherein the impregnated zonearound the cable is hydrophobic.
 29. The method according to claim 27wherein the impregnated zone around the cable includes a corrosioninhibiting material.
 30. The method according to claim 27 wherein theimpregnated zone around the cable has an increased electricalresistance.
 31. The method according to claim 27 wherein the impregnatedzone around the cable has a reduced permeability.
 32. The methodaccording to claim 27 wherein the fluid comprises a liquid which isarranged to increase in viscosity after inserting into the cable. 33.The method according to claim 27 wherein the fluid is a liquid which isarranged to set-up after inserting into the cable.
 34. The methodaccording to claim 27 wherein the fluid comprises a liquid selected fromthe group consisting of: Silane, siloxane, silicone, Organofunctionalsilane, Oil, Mineral oil, Calcium sulfonate, and Polymer resin.